One of the main types of prior art magnetic bubble stores comprises an assembly of loops or registers, known as minor loops, for storing information, this assembly being associated with one or two loops or registers, known as major loops, forming the store access stations. The minor loops are disposed longitudinally, one beside the other, the major loops being orientated perpendicularly to the minor loops. The magnetic bubbles in the minor loops can be transferred to the major loops and vice versa, via the agency of unidirectional or bidirectional transfer gates.
When a single major loop is used, the reading and writing of the information is carried out by means of that single loop. In the first case we speak of a store having a major-minor organization. On the other hand, when two major loops are used, the writing of the information is performed via the agency of one of the two loops, the reading of the information being performed by the agency of the other loop. These major loops are generally situated on either side of the minor loops. In the latter case (two loops), we generally speak of a memory having a series-parallel organization.
In the bubble stores described above, a bubble is produced on a major loop, corresponding to the writing of information, by applying a high current to a generally U-shaped conductor (FIG. 1) passing through the propagation motifs forming the major loop. This operation, generally known as nucleation, is performed when the bubble is in a cavity defined between two adjacent motifs.
After nucleation, the bubble is then propagated by the application of the rotary field H.sub.T on the major loop towards the transfer gates, so as to transfer the bubble from the major loop to a minor loop. The transfer gates generally take the form of a U-shaped conductor. The application of a current pulse to the conductor enables each bubble to be extended between the apexes of the propagation motifs of the major loop and the corresponding ones of the minor loop, whereafter the stoppage of the current pulse produces the contraction of the bubbles on the minor loop. The transfer is then carried out. The information is thus stored on the minor loop.
The reading of the information is performed by transferring a magnetic bubble from a minor loop to a major loop. The transfer is carried out as before.
To perform non-destructive reading of information, the corresponding bubble must be duplicated. In the case of a bubble-for-bubble duplication, such duplication is produced by means of a conductor (FIG. 1) extending through the major loop, to which a current pulse is applied, causing the elongation of the bubble on either side of the propagation paths, and then the cutting of the bubble into two. One of the bubbles, transferred over a detection path, can be destructively detected by a magneto-resistive type detector, generally on an iron and nickel base, and the other bubble will be reinjected into the minor loop at the place occupied by the original bubble.
A bubble store operating on this principle was described in U.S. Pat. No. 4,253,159, filed on Dec. 3, 1979, and entitled "Ion-implanted bubble memory with replicate port". In that patent use is made of a single major loop and non-implanted propagation motifs.
Magnetic bubble stores having non-implanted motifs as propagation motifs and having a structure and operation such as those disclosed hereinbefore (cf. the U.S. Patent) have two important limitations, namely information access time and information flow.
To solve these problems, one approach consists in dividing the bubble store into a number of identical storage devices or elements operating in parallel on the same chip; such independent devices or elements have any organization, for example, a series-parallel or a major-minor organization. The flow of information, which is proportional to the number of storage detectors, is then increased and the information access time diminished, seeing that the storage zone of each device is reduced. Such a storage structure is disclosed in an article by P. K. GEORGE, H. S. GILL, R. H. NORTON, G. F. REYLING, A. M. TUXFORD, which appeared in Intermag Conference Digest, GRENOBLE 1971, Paper No. 9-1.
Although this method enables the performances of the store to be improved (flow, access time), this storage organization or structure requires a number of control circuits proportional to the number of storage devices or elements contained in the chip, and more particularly as regards the multiplicity of the detection circuits of the bubbles; the use of several control circuits considerably increases the manufacturing cost of the store.